The aim of the present project is to establish a fundamental understanding of how the interplay between adsorption of simple gas-phase molecules and doping may be employed to fine-tune the function of small silicon clusters. Due to the intricate relationship between the geometric and electronic structure of clusters in the sub-nm size range a reliable determination of the corresponding ground-state geometric structures is a prerequisite. A major aspect of theproject is therefore to develop and employ efficient unbiased sampling techniques based ondensity-functional theory for this class of systems. The main objective is to use the obtained detailed geometric, energetic and electronic structure data to establish a trend understanding of stable adsorbate/dopant combinations with interesting materials properties. Contact to experiment, also for method validation, is particularly sought through the computation of vibrational fingerprints and X-ray absorption spectra.